<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    body>div {
      width: 200px;
      height: 200px;
      border: 1px solid red;
    }
    #d1 {
      width: 50px;
      height: 50px;
      background-color: red;
    }
    #d2 {
      width: 50px;
      height: 50px;
      background-color: green;
    }
    #d3 {
      width: 50px;
      height: 50px;
      background-color: blue;
    }

    ul {
        list-style-type: none;
        margin: 0;
        padding: 0;

    }
    li {
        float: left;
        margin-right: 20px;
    }

  </style>
</head>
<body>
<ul>
    <li><a href="">首页</a></li>
    <li><a href="">免费课</a></li>
    <li><a href="">直播课</a></li>
    <li><a href="">线上班</a></li>
    <li><a href="">线下班</a></li>
</ul>
<div>
  <div id="d1"></div>
  <div id="d2"></div>
  <div id="d3"></div>
</div>
</body>
</html>